1. Field of the Invention
The present invention relates to a compact reactor having a simplified structure and also having a good high frequency characteristic.
2. Description of the Prior Art
The reactor has hitherto been desired to be of a design, in which it can be incorporated in various inverter or the like to remove, for example, switching noises, has a high performance, along with a compact size and a low cost, and a simplified structure and an easiness to manufacture. In the reactor as shown in FIG. 6A, the resonance frequency f0 at which resonance takes place at the inductance L and distributed capacitance C0 of the winding unit (coil) is expressed by the following equation and, when the frequency is lower than the resonance frequency f0, the winding unit acts as a reactor:f0=1/(2π(L·C0)1/2)
In general, in order to obtain the reactor which is compact in size and low in cost and has a high inductance L, in the case of a multilayer winding method of forming the reactor by winding a round sectioned copper wire helically in a number of layers, the distributed capacitance C0 of the resultant coil tends to become high and the resonance frequency f0 tends to become low and the winding does no longer function as a reactor at a high frequency region, accompanied by reduction of the high frequency characteristic. On the other hand, at the low frequency region, if the number of windings increase, the direct current resistance Rdc of the winding becomes high, accompanied by an increase of the current loss or the like. On the other hand, lowering of the direct current resistance Rdc require the use of a wire thick enough to make it difficult to wind and also to compactize.
In the meantime, as a reactor having a good high frequency characteristic, the reactor of a rectangular sectioned flat wire wound type or a rectangular wire spirally wound type, in which the rectangular wire having a large width for a given thickness is wound spirally has hitherto been well known in the art. See, for example, the Patent Document 1 listed below. In this edgewise winding, since the distributed capacitance is so small that the resonance frequency f0 becomes high and, therefore, the reactor excellent in high frequency characteristic can be obtained.
The reactor of a structure, in which the rectangular wire is wound a number of turns in overlapped fashion and which has a volumetric efficiency comparable to that of the edgewise winding, has also been known in the art. See, for example, the Patent Document 2 listed below.    [Patent Document 1] JP Laid-open Patent Publication No. H10-97927    [Patent Document 2] JP Laid-open Patent Publication No. 2003-124039
It has, however, been found that the edgewise winding requires the use of a substantial length of a winding wire for the coil in order to secure a high inductance. To reduce the length of the winding wire the use of the rectangular wire having a large vertical to lateral ratio (ratio between the height and the width) and, therefore, it is impossible to reduce the size of and the cost of the reactor. On the other hand, the rectangular wire requires a high cost and requires an increased number of assembling steps, accompanied by a low yield. Also, even where the volumetric efficiency comparable to that achieved by the edgewise winding is achieved by the use of the rectangular wire, simplification of the structure and reduction in cost cannot be accomplished sufficiently.